A comparison in a lung model of low- and high-flow regulators for transtracheal jet ventilation

There is widespread agreement that transtracheal jet ventilation (TTJV) using a percutaneously inserted intravenous (iv) catheter through the cricothyroid membrane is a simple, quick, relatively safe, and extremely effective treatment for the situation in which neither ventilation nor intubation can be achieved. No study has reported whether a low-flow pressure-reducing regulator (LFR) can provide enough driving pressure and flow under a variety of clinical circumstances for adequate TTJV. We determined, using a high-flow regulator (HFR) as our control, the tidal volume (VT) (measured by integrating a pneumotachograph signal) that a LFR could deliver via a Carden jet injector through 14- and 20-G iv catheters initially at an inspiratory:expiratory ratio (I:E) = 1:1 (unit of time = 1 s) in a mechanical model that had varying lung compliance (Cset, 10-100 ml/cmH2O) and airway diameters (proximal trachea 15.0, 4.5, or 3.0 mm ID and distal mainstem bronchi 9.0 or 4.5 mm ID). The lowest Cset (10 ml/cmH2O) and smallest airway diameter (tracheal diameter = 3.0 mm, bronchial diameter = 9.0 mm) resulted in the lowest VT (220 and 320 ml for the 20- and 14-G iv catheters, respectively, with the LFR), and the highest Cset (100 ml/cmH2O) and largest airway diameter (tracheal diameter = 15 mm, bronchial diameter = 9.0 mm) resulted in the highest VT (780 and 1040 ml for the 20- and 14-G iv catheters, respectively, with the LFR). The VT produced during TTJV was greatly dependent on air entrainment (measured by a second pneumotachograph), with the contribution to total VT ranging from 15 to 74%; the amount of air entrainment was independently confirmed by excellent agreement between measured and calculated alveolar oxygen concentrations. Decreasing Cset (with the largest airway diameter) and decreasing airway diameter (at Cset = 50 ml/cmH2O) over the full range studied resulted in approximately a 45-80% decrease in VT for all iv catheter/regulator combinations. Increasing Cset and narrowing airway diameter over the full range studied resulted in a progressive increase in end-expiratory volume (EEV) for all iv catheter/regulator combinations. The I:E ratio was also varied from 1:3 to 3:1 (unit of time = 1 s) using the 14-G catheter at Cset = 50 ml/cmH2O with both regulators at the extremes of the proximal tracheal diameters (15.0 and 3.0 mm ID), and we found that jet ventilation through a proximal tracheal diameter of 3.0 mm with the HFR at I:E ratios = 1:1 and 3:1, EEV exceeded the capacity of the mechanical lung (4,000 ml).(ABSTRACT TRUNCATED AT 400 WORDS)